1. Field of Invention
The present invention pertains to the field of electronic circuits. More particularly, this invention relates to digital integration of wide dynamic range, high bandwidth signals.
2. Art Backaround
It is often useful in electronic systems to integrate an electrical signal. For example, an integration of an electrical signal may be useful in electronic systems that measure the emission of electrons or emission of various types of quantized radiation. Typically, a detector in such systems generates an electrical signal in response to a quantized emission. An integrator may be useful in such a system for determining a quantization count or an intensity value by integrating the electrical signal generated by the detector.
Prior integrators are typically realized using an analog circuit which includes an amplifier and a capacitor having a feedback configuration. Typically, an electrical signal being integrated is applied to an input of the amplifier and an electrical charge accumulates on the capacitor in response to the electrical signal. Typically, the integral of the electrical signal is indicated by an amount of electrical charge accumulated on the capacitor. The capacitor in an analog integrator must usually be discharged or reset prior to an integration operation.
Unfortunately, such analog integrators may be subject to errors caused by a residual charge on the capacitor. Such a residual charge may be caused by an incomplete discharge during reset of the capacitor. Moreover, such prior integrators may be subject to errors caused by leakage in the capacitor or charge accumulation on the capacitor due to bias currents in the amplifier.
In addition, the time required to discharge the capacitor may be relatively long due to the R-C time constant inherent in an analog integrator. Unfortunately, a relatively long discharge time usually limits the speed at which successive integration operations may be undertaken. Such a limitation may render such analog integrators unsuitable for systems in which the amount of time between integration intervals is very brief and in which the dynamic range of the electrical signal being integrated is relatively wide.
For example, an electronic system that measures light emitting from a surface commonly subdivides the surface into an array of pixel areas. Typically, such a system successively samples the light emitting from the pixel areas according to a particular pixel scan rate. In systems with a relatively high pixel scan rate the time between adjacent pixel areas is relatively brief. As a consequence, successive integration operations on an electrical signal that carry measurements from adjacent pixels must usually be undertaken relatively quickly. Unfortunately, analog integrators usually cannot be reset quickly enough to avoid integration errors caused by an incomplete capacitor discharge.
Moreover, such problems are usually worsened for signals having a wide dynamic range. Typically, an integration operation on a signal having a wide dynamic range using an analog integrator involves relatively long integration times and higher levels of charge accumulation on the capacitor. Such conditions typically increase the time required for capacitor discharge in preparation for the next integration interval. This usually slows the rate at which integration operations may occur and increases the likelihood of errors cause by incomplete capacitor discharge.